Palynological data review of selected boreholes in the Great Artesian, Lake Eyre basins and Upper Darling Floodplain (part 2) ‒ Infilling data and knowledge gaps

This report presents palynological data compiled and analysed as part of the National Groundwater Systems (NGS) Project. NGS is part of Exploring for the Future (EFTF)—an eight year, $225 million Australian Government funded geoscience data and information acquisition program focused on better understanding the potential mineral, energy and groundwater resources across Australia. This study builds on previous work (Hannaford et al., 2022) undertaken as part of the ‘Assessing the Status of Groundwater in the Great Artesian Basin’ project, commissioned by the Australian Government through the National Water Infrastructure Fund – Expansion. The study undertaken by MGPalaeo, in collaboration with Geoscience Australia, examined an additional 688 boreholes across the GAB and compiled 149 new palynological summary sheets having Jurassic‒Cretaceous succession, with reviewed palynology data (down to total depth). The combined borehole palynological data examined from this study and the previous GAB work (Hannaford et al., 2022) is compiled in Appendix B4. The combined dataset totals 1,394 boreholes examined and 652 with palynology in the stratigraphic interval of interest, 102 of these boreholes contained Cenozoic palynology relevant to the Lake Eyre Basin. This information has been used to revise stratigraphic correlations across the GAB (Norton & Rollet, 2022 and 2023). Initial review of the stratigraphy in the Lake Eyre Basin (LEB) compiled existing palynology from outcrop, mineral and petroleum boreholes. An additional 28 boreholes in the Upper Darling Floodplain region were examined, 16 of which contained relevant palynology. The main palynological data infill in the GAB and LEB region during this follow-up study focused on: 1. Collecting, processing and analysing new biostratigraphic data on 149 key boreholes particularly across the Eromanga and Surat basins boundary. The study focussed on integrating data in New South Wales from the southern Surat Basin and central Eromanga Basin. 2. Further palynological data infill and palynological analysis on 15 samples from 7 boreholes in the western Eromanga Basin to assess difficulties in correlating the stratigraphy across the Algebuckina Sandstone. 3. Compiling existing analyses and update any historical palynological data in the Lake Eyre Basin to reflect the latest zonation scheme developed in this study. The new palynological data combined with new zircon data from other studies in the Carpentaria and Surat basins (Foley et al., 2020, 2021, 2022; La Croix et al., 2022, respectively) provides information on the tie to the geological timescale and help refine the chronostratigraphic chart that summarises stratigraphic correlations across the Carpentaria, Surat and Eromanga basins of Hannaford et al. (2022). All boreholes were examined outside of the Cooper and Bowen basins boundaries with selected boreholes around transects defined for stratigraphic correlation review through the Cooper and Bowen basin outlines (Norton & Rollet, 2022 and 2023). As a result, most of the remaining unreviewed palynological data lies within the Cooper and Bowen basins. The results of the palynology data infill in the western Eromanga Basin, in South Australia and Northern Territory, show that the Algebuckina Sandstone section is dominated by clean sandstone and so the cuttings samples were also dominated by sand. Although attempts were made to concentrate the shale from the cuttings in the thicker shale mid formation, this did not yield results, due to the amount of caved Cretaceous material. An initial assessment of the Lake Eyre Basin palynological data and zonation scheme was undertaken using information derived from water, mineral and petroleum boreholes. This provides an initial state of knowledge for the Lake Eyre Basin that can be built on in the future. Recommendations are provided for further studies to build a better understanding of the stratigraphy in the Great Artesian and Lake Eyre basins.